The invention describes a process for decreasing the amount of mercaptans in petroleum streams, particularly naphtha streams.
Future environmental regulations will require significantly lower sulfur levels in motor gasoline. The proposed regulations will require the complete desulfurization of cat naphtha, which contains the vast majority of the sulfur in gasoline. There is a large economic incentive to remove or reduce the sulfur in cat naphtha while retaining olefins which are important for octane. Selective cat naphtha hydroprocessing requires the selective conversion of organosulfur to hydrogen sulfide (HDS) while minimizing olefin saturation (SAT).
In the late ""30""s, ""40""s and early ""50""s, before the advent of large scale fluid cat cracking (FCC), a range of improved technologies for extracting C6 to C9 mercaptan sulfur from thermal cracked naphtha were developed. These technologies were required because mercaptan and disulfide sulfur had a strong negative interaction with tetraethyl lead, which was then used in considerable quantities to improve gasoline octane. These technologies relied on solutizing additives, such as methanol, ethanol, or isopropanol to significantly improve the extractability of gasoline range mercaptans. With the advent of FCC technology, the solutizing technologies were no longer required since FCC does not produce mercaptans in this product range.
Several references teach the removal of mercaptans and phenolic compounds from petroleum distillates. For example, U.S. Pat. No. 2,309,651 teaches the use of a countercurrent extraction utilizing an alkaline reagent and solvent such as methanol. Although the reference teaches other alcohols, such as ethanol, propanol, isopropanol etc., methanol is preferred.
U.S. No. 2,347,348 teaches the removal of mercaptans from gasoline utilizing a caustic methanol solution. Though the reference speaks of other suitable organic solvents such as ethanol, propanol, acetone, ethylene glycol etc. methanol is the preferred solvent.
What is needed in the art is a method for economically and effectively removing mercaptans from petroleum streams.
The invention includes a method for decreasing the amount of mercaptans in a petroleum stream comprising the steps of:
(a) extracting said petroleum stream containing mercaptans with an extractant comprising ethanol and an aqueous base to produce a product having a decreased concentration of mercaptans and a used extractant comprising said extracted mercaptans, ethanol and base;
(b) recovering said product having a decreased amount of mercaptans.
Surprisingly, applicants have discovered that when ethanol is utilized in conjunction with a base to extract mercaptans from a hydrodesulfurized petroleum stream, or a petroleum stream containing mercaptans, it is much more effective than other alcohols, including methanol, which is taught as the preferred alcohol in the solutizing art. Furthermore, since ethanol is a beneficial component of mogas, the instant extraction method is economical and practical.